Conveyors utilizing live rollers that rotate about a fixed axle are known in the art. The rollers may be rotated by, e.g., a belt that engages the outer surface of the rollers (see, U.S. Pat. No. 6,685,005), by a rotating line shaft operatively connected to the rollers by O-rings (see U.S. Pat. No. 5,042,644), or by internal motors.
Some rollers for roller conveyors utilize a stub shaft axle at each end for the fixed axle. See, e.g., U.S. Pat. No. 4,681,215, which discloses a conveyor roller rotatable about a pair of fixed stub axles, each axle having a pair of self-aligning bearing assemblies associated therewith.
However, advantages accrue to conveyor rollers that utilize a single axle that extends the full-width of the roller and whose ends are mounted in the side frame members of the conveyor. Specifically, a full-width axle may be spring loaded in order to facilitate quicker removal and installation. Also, a full-width axle requires only a single roller bearing assembly per side, while the use of stub shafts normally requires two bearing assemblies per side.
Full-width axles do, however, entail certain potential disadvantages. Such full-width axles may tend to sag or bow in the middle, the degree to which this occurs being a function of the length of the axle. The bowing causes misalignment of the ends of the axle with respect to their bearings, cocking the inner bearing race, and pinching the ball bearings between the inner and outer races of the bearing assembly, thus exacerbating the wear on the bearings. Consequently, the capacity of the roller conveyor dramatically decreases as the width of the rollers increases.
This is particularly problematic in the context of a belt conveyor, where it is highly desirable to have a small diameter end pulley to minimize the gap between the conveyor beds and to minimize transition problems from conveyor to conveyor. This is especially important when small packages are being conveyed, as they could fall in the gap between the industry-standard 4 inch diameter pulleys used at transition sections. Presently, in order to avoid this problem, a small, non-powered gap roller is placed between the transition pulleys. However, a small box can stall out or skew, causing problems.
The industry trend is to try to utilize transition rollers having diameters smaller than the standard 4 inches, but there are difficulties. Specifically, when a small diameter is utilized, the bearing used requires a small axle, which cannot take the deflection, especially at widths over 24 inches and at higher belt pulls. To overcome this problem, some have utilized “step shafts,” in which the inner part of the axle is a larger diameter of machined steel, and the ends are machined down to fit in the bearing. However, this has proven to be very expensive and not commercially feasible. Others have used solid steel DOM (Drawn Over Mandrel) tubes inside the rollers as axle stiffeners, but at the current price of steel, it is economically impractical.
Accordingly, it is an object of the present invention to provide a conveyor roller with a full-width axle in which the axle does not sag or bow. More specifically, it is an object of the present invention to provide a reinforcing member or sleeve for the axle of a roller conveyor that substantially eliminates sagging or bowing of the axle.